1. Field of the Invention
The present invention relates to overload protectors for communications systems and in particular, to overvoltage protection devices that are impervious to the weather which also may include back-up and overheat protection.
2. Discussion of the Relevant Art
In communication systems, such as telephone systems, it is necessary to position overload protectors at various positions to protect sensitive parts of the system and to protect equipment attached to the line from lightning strikes or other causes of overvoltage appearing on the communication lines. Typically these overvoltage protection devices incorporated the carbon block type which provided a parallel air spark gap that would break down at a predetermined voltage. However, the carbon block protectors would degrade during normal operation on the communication line and cause static to appear thereon. Later, gas protection devices which used thermally sensitive plastics were assembled with spring pressure on them and thus, when overheated would yield and short the terminal line to ground.
With the inherent desire to protect the communication equipment several different types of protectors have been used over the years, each including thermally active members which when overheated causes the line terminals to short to ground (fail short). Initially the thermally sensitive material was a low temperature melting solder pellet, which when melted because of extreme heat caused by an overvoltage, would permit the housing in some manner to short the line terminal to ground. Further improvements in the state of the art replaced the solder pellet used with the gas filled tube. Still further improvements of the protection devices, which proved to be more reliable utilized a back-up air gap together with the thermally sensitive material used for overheating protection in the assemblies.
U.S. Pat. No. 5,224,013, issued Jun. 29, 1993 to Emanual J. Pagliuca and entitled "Miniature Station Protector Modules" overcame the shortcomings of the prior art in most respects, however, that device was not weatherproof since the line terminals were completely exposed to the environment.
Moreover, all of the known devices required that the technician in replacing any of the components after a lightning strike or overvoltage condition to carefully replace the components as it was originally assembled so that the protection would be restored. This type of assembly work performed in the field proved to be a handicap and thus it was found more desirable to provide a device which is completely sealed and when it has provided its useful protection is just thrown away and replaced with a new unit. This, of course, became feasible only with the advent of inexpensive thermally sensitive plastics and a new type of construction which reduced the cost of the protection device.
In addition, it was a design goal to make the assembly weatherproof or impervious to weather conditions so that the units that were installed on the outside of buildings and/or exposed to the environment would not inadvertently cause shorts to the telephone terminal lines by providing a moisture path to ground.
Therefore, it is an object of the present invention to provide a weatherproof station protector module for communication system which is completely sealed and may be disposed of once it has served its purpose for protecting the communication line.
It is another object of the present invention to provide a weatherproof station protector module which combines all of the features of the earlier type devices including fail-safe shorting, with a back-up air gap arrangement that is coupled to the line terminals, highly stable and efficient, as well as being inexpensive to manufacture.
It is still a further object of the present invention to provide a weatherproof station protector module which is capable of using a gas tube surge protector device as well as, solid state protector devices.
The foregoing and other object and advantages will appear from the description to follow. In the description reference is made to the accompanying drawing which forms a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the spirit and scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is best defined by the appended claims. Like reference characters have been utilized to designate like or corresponding components in the alternative embodiments in order for the reader to better understand the invention.